Momentum-Resolved Lifetimes of Image-Potential States on Cu(100)

Abstract

The dependence of the inelastic lifetime of electrons in the image-potential states of Cu(100) on their momentum parallel to the surface has been studied experimentally by means of time- and angle-resolved two-photon photoemission and theoretically by evaluating the electron self-energy within the $\mathrm{GW}$ approximation. The pronounced decrease of the $n\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1$ lifetime from 40 fs at normal emission $({k}_{\ensuremath{\parallel}}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0)$ to 20 fs for ${k}_{\ensuremath{\parallel}}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.33{\AA{}}^{\ensuremath{-}1}$ cannot be accounted for by interband decay processes to bulk states. We show that intraband transitions within the image-state band give a contribution to this decrease comparable in magnitude with the interband channel.